U.S. patent application number 10/415097 was filed with the patent office on 2004-05-20 for linear actuator.
This patent application is currently assigned to THK CO., LTD. Invention is credited to Furusawa, Ryuji, Iida, Katsuya, Kadono, Toshiaki, Kawakami, Takeomi.
Application Number | 20040093970 10/415097 |
Document ID | / |
Family ID | 19089149 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040093970 |
Kind Code |
A1 |
Iida, Katsuya ; et
al. |
May 20, 2004 |
Linear actuator
Abstract
A linear actuator realizing low generation of dust and low
generation of noise and bearing a large axial load is provided. A
plurality of spacers 30, - - - , each having at its both ends
spherical recessed portions corresponding to curved surfaces of
balls 28, - - - , are arranged between the balls 28, - - - of the
guide portion of the linear actuator, and the spacers 30, - - - are
connected to each other in series by belt-shaped members 31 having
flexibility. On the other hand, a plurality of spacers 35, - - - ,
each having at its both ends spherical recessed portions
corresponding to curved surfaces of balls 33, - - - for the screw
shaft of a screw portion, are arranged between the balls 33, - - -
in a manner separated from each other. By selecting a retainer 27
and the spacer 35 in accordance with the shapes of the guide
portion and the screw portion, unnecessary contacting of the mutual
balls and unnecessary contacting of the balls to the surrounding
circulation passage can be prevented, thus realizing low generation
of dust and low generation of noise.
Inventors: |
Iida, Katsuya; (Yamanashi,
JP) ; Kadono, Toshiaki; (Yamanashi, JP) ;
Kawakami, Takeomi; (Yamanashi, JP) ; Furusawa,
Ryuji; (Yamanashi, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
THK CO., LTD
11-6, Nishi-gotanda 3-chome, Shinagawa-ku
Tokyo 141-0031
JP
|
Family ID: |
19089149 |
Appl. No.: |
10/415097 |
Filed: |
April 30, 2003 |
PCT Filed: |
July 31, 2002 |
PCT NO: |
PCT/JP02/07771 |
Current U.S.
Class: |
74/89.33 ;
384/51; 74/424.88 |
Current CPC
Class: |
Y10T 74/19777 20150115;
F16C 29/063 20130101; F16H 25/2233 20130101; F16C 29/0607 20130101;
F16H 2025/2242 20130101; F16H 25/24 20130101; Y10T 74/18656
20150115; F16C 33/3706 20130101; F16C 33/3825 20130101 |
Class at
Publication: |
074/089.33 ;
074/424.88; 384/051 |
International
Class: |
F16H 003/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2001 |
JP |
20011-262222 |
Claims
1. A linear actuator comprising a track member, having U-shape in
section, provided with inner wall surfaces opposing to each other,
a movable member disposed between the inner wall surfaces and a
screw shaft penetrating the movable member, in which rolling member
rolling portions are formed on the inner wall surfaces of the track
member; loaded rolling member rolling portions are formed on both
side surfaces of the movable member so as to correspond to the
rolling member rolling portions; rolling member return passages
extending in parallel to each other with a predetermined distance
from the loaded rolling member rolling portions and direction
changing passages each connecting the loaded rolling member rolling
portions and the rolling member return passages are formed in the
movable member so as to circulate the rolling members rolling
between the rolling member rolling portions and the loaded rolling
member rolling portions; a rolling member rolling portion for the
screw shaft in form of spiral is formed to an outer peripheral
surface of the screw shaft; a loaded rolling member rolling passage
for the screw shaft is formed on the through hole formed in the
movable member so as to correspond to the rolling member rolling
portion of the screw shaft; and a rolling member return passage for
circulating the rolling member for the screw shaft rolling between
the rolling member rolling portion for the screw shaft and the
loaded rolling member rolling portion for the screw shaft is formed
in the movable member, wherein a plurality of spacers, each having,
at both ends thereof, curved recessed portions corresponding to
curved surface of the rolling member are arranged between the
rolling members, the plural spacers being connected in series by
belt-shaped members having flexibility; a plurality of spacers,
each having, at both ends thereof, curved recessed portions
corresponding to the curved surface of the rolling member, are
disposed between the rolling members for the screw shaft in a
manner separated from each other; and a holding member extending
along both side edges of the loaded rolling member rolling portion
is mounted to the movable member for preventing the rolling member
held by the belt-shaped members and the spacers from coming off at
a time when the movable member is removed from the track
member.
2. The linear actuator according to claim 1, wherein the rolling
member rolling passage composed of the loaded rolling member
rolling passage, the rolling member return passage and the
direction changing passage is provided with a guide portion for
guiding the belt-shaped member.
3. The linear actuator according to claim 1 or 2, wherein the
return passage constituting member constituting the return passage,
the direction changing inner periphery side constituting member
constituting the inner periphery side of the direction changing
member, the direction changing outer periphery side constituting
member constituting the outer periphery side of the direction
changing member, and the holding member are formed from resin
material independent from a body portion of the movable member.
Description
TECHNICAL FIELD
[0001] The present invention relates to an actuator comprising a
track member having substantially U-shape in section and a movable
member integrally provided with guide portions formed on both side
surfaces thereof and a ball screw portion formed in a central
portion thereof.
BACKGROUND OF THE INVENTION
[0002] As shown in FIG. 11, there is known a linear actuator
provided with an outer rail 1 having substantially U-shape and an
inner block 2 disposed inside the outer rail 1 and integrally
provided with guide portions 2a, 2a formed on both side surfaces
thereof and a ball screw portion 2b formed in a central portion
thereof.
[0003] The guide portions 2a, 2a have the following structures. The
outer rail 1 has a pair of opposing inner wall sections 1a, 1a, on
which upper and lower two rows of ball rolling grooves 1b, 1b are
formed, respectively. On the other hand, the inner block 2 disposed
inside the outer rail 1 has both side surfaces, on which loaded
ball rolling groove 2c, 2c are formed so as to oppose to the ball
rolling grooves 1b, 1b, and a number of balls 3, 3, - - - are
disposed to be movable between the mutually opposing ball rolling
grooves 1b, 1b and loaded rolling grooves 2c, 2c.
[0004] The screw portion 2b, on the other hand, has the following
structure. A screw shaft 4 penetrates the central portion of the
inner block 2. The screw shaft 4 is formed, on its outer peripheral
surface, with a spiral ball rolling groove. A spiral loaded ball
rolling groove corresponding to this spiral ball rolling groove is
formed on a through hole of the inner block 2.
DISCLOSURE OF THE INVENTION
[0005] Since such a linear actuator has a integrally-provided guide
portions 2a, 2a and ball screw portion 2b, the actuator provides
functions, as actuator, of high rigidity and high performance in
the minimum space. Accordingly, such linear actuator has been
mainly utilized for a semiconductor manufacturing system or a
liquid crystal manufacturing system, or under a clean environment
in a medical or like equipment. For such clean environment, it is
required to generate less dust or less noise, or like.
[0006] In order to reduce the dust to be generated from the
actuator, a driving portion including a guide member of the
actuator is covered by a case, to which air-sucking may be further
conducted. However, even if the driving portion including the guide
member is covered by the case, dust is yet generated from a sliding
portion, therefore it is not fundamentally solution.
[0007] Moreover, a preload is applied to the ball screw portion 2b
of the linear actuator for enhancing the positioning performance.
The inner block 2 of the linear actuator is, however, different
from a ball screw composed of a screw shaft and a nut, and has a
structure in which the guide portions 2a, 2a and the ball screw
portion 2b are integrally formed. According to such structure, in a
manufacturing process, there is not adopted a method or system for
applying a preload, as like a general ball screw, by displacing a
phase of a ball rolling groove formed to the nut, and in
substitution therefor, there is adopted an over-size preloading
method or system in which over-sized balls, each having a diameter
slightly larger than a gap between the screw shaft 4 and the inner
block 2, are arranged. In the case where this over-size preloading
method is adopted, a spacer ball, having a diameter slightly
smaller than that of the over-size ball, is arranged between the
over-sized balls for smooth circulation of the balls. However, the
arrangement of such spacer balls reduces the number of the balls to
which load is applied, and load in the axial direction to be loaded
will be reduced.
[0008] Then, the present invention has an object to provide a
linear actuator which can realize reduced dust generation and low
noise generation and providing a large load in the axial direction
to be loaded.
[0009] The present invention will be explained hereunder, in which
although reference numerals on the accompanying drawings are added
with parentheses in order for easy understanding of the invention,
the present invention is not limited to an embodiment illustrated
in the drawings by the added reference numerals.
[0010] The inventor of the subject application conceived to locate
spacers between rolling members at a guide portion and a screw
(thread) portion, the spacer having recessed portions, on both end
portions of a rolling member, each having a shape corresponding to
a curved surface of the rolling member, in order to prevent metal
contact of the rolling members and to perform smoothly arranged
movement of the rolling members. Furthermore, in view of the fact
that circulation motion of the rolling member at the guide portion
is a two-dimensional motion in a plane in which a linear loaded
rolling passage and a linear return passage are connected through a
U-shaped direction changing passage and the circulation motion of
the rolling member at the screw portion is a complicated spiral
three-dimensional motion, there was conceived that a plurality of
spacers arranged in the guide portion are connected to each other
in series by means of belt-shaped member and a plurality of spacers
arranged in the screw portion are, on the contrary, separated from
each other, thus preventing the rolling members from contacting
with the circulation passages surrounding the rolling members.
[0011] More specifically, the above object can be achieved by
providing a linear actuator of the invention of claim 1, which
comprises a track member (7), having U-shape in section, provided
with inner wall surfaces (7a, 7a) opposing to each other, a movable
member (8) disposed between the inner wall surfaces (7a, 7a) and a
screw shaft (9) penetrating the movable member (8), in which
rolling member rolling portions (11) are formed on the inner wall
surfaces of the track member (7); loaded rolling member rolling
portions (19) are formed on both side surfaces of the movable
member (8) so as to correspond to the rolling member rolling
portions (11); rolling member return passages (C) extending in
parallel to each other with a predetermined distance from the
loaded rolling member rolling portions (19) and direction changing
passages (B) each connecting the loaded rolling member rolling
portions (19) and the rolling member return passages (C) are formed
in the movable member so as to circulate the rolling members (28, -
- - ) rolling between the rolling member rolling portions (11) and
the loaded rolling member rolling portions (19); a rolling member
rolling portion (9a) for the screw shaft (9) in form of spiral is
formed to an outer peripheral surface of the screw shaft (9); a
loaded rolling member rolling passage (15a) for the screw shaft is
formed on the through hole formed in the movable member so as to
correspond to the rolling member rolling portion (9a) of the screw
shaft; and a rolling member return passage (E) for circulating the
rolling member (33, - - - ) for the screw shaft rolling between the
rolling member rolling portion (9a) for the screw shaft and the
loaded rolling member rolling portion (15a) for the screw shaft is
formed in the movable member,
[0012] wherein a plurality of spacers (30, - - - ), each having, at
both ends thereof, curved recessed portions (30a, - - - )
corresponding to curved surface of the rolling member (28,- - - )
are arranged between the rolling members, the plural spacers (30, -
- - ) being connected in series by belt-shaped members (31, 31)
having flexibility;
[0013] a plurality of spacers (35, - - - ), each having, at both
ends thereof, curved recessed portions corresponding to the curved
surface of the rolling member (33, - - - ), are disposed between
the rolling members for the screw shaft in a manner separated from
each other; and
[0014] a holding member (17) extending along both side edges of the
loaded rolling member rolling portion (19) is mounted to the
movable member (8) for preventing the rolling member (28, - - - )
held by the belt-shaped members (31, 31) and the spacers (30, - - -
) from coming off at a time when the movable member (8) is removed
from the track member (7).
[0015] According to the present invention, a plurality of spacers,
having curved recessed portions corresponding to the curved
surfaces of the rolling members, are disposed between the rolling
members of the guide portion and the screw portion, so that the
mutual contact between the respective metal rolling members can be
prevented. Furthermore, since the plural spacers arranged in the
guide portion, in which two-dimensional motion is carried out, are
connected to each other in series by the belt-shaped members, the
rolling members circulate in the constant track, and unnecessary
contacting of the rolling members and their surrounding circulation
passage can be prevented. In the screw portion, on the other hand,
the twisting motion around the advancing direction is required as
well as the two-dimensional and three-dimensional direction
changing motions, so that unnecessary contacting of the rolling
members and their surrounding circulation passage can be prevented
by separating the spacers without connecting the spacers by the
belt-shaped members. Thus, since the mutual contact of the rolling
members and the unnecessary contacting of the rolling members and
their surrounding circulation passage can be prevented, low
generation of dust or like and low generation of noise can be
realized.
[0016] Still furthermore, by arranging the spacers, each having
curved recesses at its both end portions corresponding to the
curved surface of the rolling member, the distance between the
adjacent balls can be shortened in comparison with the case of
using the spacer balls, for example. Accordingly, there is provided
a linear actuator having a large axial load to be applied.
[0017] The invention of claim 2 is characterized, in the linear
actuator of claim 1, in that the rolling member rolling passage
composed of the loaded rolling member rolling passage (19, A), the
rolling member return passage (C) and the direction changing
passage (B) is provided with a guide portion (16a, 26) for guiding
the belt-shaped member (31, 31).
[0018] According to this invention, since the belt-shaped member is
guided by the guide portions provided for the rolling member
circulation passage, the belt-shaped member circulates in the more
constant track, and hence, the plural spacers connected by the
belt-shaped member and the rolling members disposed between the
spacers can be also circulated in the more constant track.
[0019] Still furthermore, according to the invention of claim 3, in
the linear actuator of claim 1 or 2, it is characterized in that
the return passage constituting member (16) constituting the return
passage (C), the direction changing inner periphery side
constituting member (25) constituting the inner periphery side of
the direction changing member (B), the direction changing outer
periphery side constituting member (18) constituting the outer
periphery side of the direction changing member (B), and the
holding member (17) are formed from resin material independent from
a body portion of the movable member (8).
[0020] According to this invention, in the guide portion, the
metallic contact is only made between the rolling member and the
rolling member rolling portion of the track and between the rolling
member and the loaded rolling member rolling portion, so that the
generation of dust and noise can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the accompanying drawings:
[0022] FIG. 1 is a perspective view, partially cutaway, showing an
essential portion of a linear actuator according to one embodiment
of the present invention.
[0023] FIG. 2 is a developed perspective view of the linear
actuator.
[0024] FIG. 3 is a plan view of the linear actuator.
[0025] FIG. 4 is a side view, partially in section, of the linear
actuator.
[0026] FIG. 5 is a sectional view taken along the line V-V in FIG.
4.
[0027] FIG. 6 is a plan view of a retainer.
[0028] FIG. 7 is a side view of the retainer.
[0029] FIG. 8 is a sectional view taken along the line VIII-VIII in
FIG. 7.
[0030] FIG. 9 is a perspective view of balls and spacers to be
accommodated in a ball circulation passage of a screw portion.
[0031] FIG. 10 is a schematic view of the balls and the retainer to
be accommodated in a ball circulation passage of a guide
portion.
[0032] FIG. 11 is a perspective view of a linear actuator of
conventional structure.
BEST MODE FOR EMBODYING THE INVENTION
[0033] FIGS. 1 to 4 represent a linear actuator according to one
embodiment of the present invention, in which FIG. 1 is a
perspective view, partially cutaway, showing an essential portion
of a linear actuator, FIG. 2 is a developed perspective view, FIG.
3 is a plan view and FIG. 4 is a side view, partially in section,
of the linear actuator.
[0034] The linear actuator is provided with an outer rail 7 as
track member having an approximately U-shaped section and an inner
block 8 as movable member disposed inside the outer rail and having
an integral structure of guide portions disposed on both side
surface sides and a central ball screw portion. When a screw shaft
9 screw-engaged with the inner block 8 is rotated by a driving
source such as electric motor, not shown, the inner block 8 is
linearly moved along the outer rail 7. In such a linear actuator,
since the guide portion and the ball screw portion are integrally
composed, functions as actuator having high rigidity and high
performance are attained in the minimum space.
[0035] Hereunder, the guide portion of the linear actuator will be
first mentioned. The outer rail 7 has an approximately U-shaped
structure having a pair of opposing inner wall surfaces 7a, 7a. The
inner wall surfaces 7a, 7a are formed with recessed grooves 10, 10
so as to extend throughout the full length thereof, and two rows of
ball rolling grooves 11, 11 are formed, as rolling member rolling
portion, at upper and lower corner portions of each of the recessed
grooves 10, 10, respectively. That is, upper and lower two ball
rolling grooves 11, 11 are formed on each of the paired inner wall
surfaces 7a, 7a of the outer rail 7 (totally, four ball rolling
grooves). Each of the ball rolling groove 11 is composed of a
so-called single circular arc groove having a curvature of its
section slightly larger than a radius of a ball. As shown in FIGS.
3 and 4, housings 13 and 14 supporting a screw shaft 9 to be
rotatable are disposed at longitudinal both end portions of the
outer rail 7. The housings 13, 14 and the outer rail 7 are
connected by fastening means such as bolts. A drive source is
mounted to the housing 13 and a joint is disposed between the screw
shaft and an output shaft of the drive source.
[0036] As shown in FIGS. 1 and 2, the inner block 8 is disposed so
as to be clamped between the inner wall surfaces 7a, 7a of the
outer rail 7. The inner block 8 comprises a block body 15, a resin
mold member (including return passage constituting member 16 - - -
and holding members 17, 17) assembled with the block body 15 and
end plates 18, 18 mounted to both end surfaces of the block body
15.
[0037] Loaded ball rolling grooves 19, 19 as upper and lower two
rows of loaded rolling member rolling grooves are formed on both
the side surfaces of the block body 15 so as to oppose respectively
to the ball rolling grooves 11, 11 of the outer rail 7. That is,
two loaded ball rolling groove 19, 19 are formed on each of the
side surfaces of the block body 15 (i.e., totally four grooves 19).
Each of these loaded ball rolling grooves is also composed of a
so-called single circular arc groove having a curvature of its
section slightly larger than the radius of the ball. A loaded ball
rolling passage as a portion of ball circulation passage (rolling
member circulation passage) in which the balls circulate is formed
between each of the ball rolling grooves 11 of the outer rail 7 and
each of the loaded ball rolling grooves 19 of the inner block
8.
[0038] FIG. 5 shows a section of the linear actuator, and with
reference to this FIG. 5, contact angle line of ball rows will be
explained hereunder. The contact angle line means, herein, a line
connecting a contact point of the ball and the ball rolling groove
11 of the outer rail 7 and a contact point of the ball and the
loaded ball rolling groove 19 of the inner block 8. In this linear
actuator, four rows of loaded ball rolling passages are formed, and
accordingly, four contact angle lines exit. The upper two contact
angle lines {circle over (1)} inclines by, for example, 45.degree.
from a horizontal line so as to be directed obliquely upward
towards the outside from the center of the actuator and the lower
two contact angle lines {circle over (2)} inclines by, for example,
45.degree. from a horizontal line so as to be directed obliquely
downward towards the outside from the center of the actuator.
According to such structure, there is provided a linear actuator
capable of bearing loads in four directions including radial
direction (lower direction), opposite radial direction (upper
direction) and horizontal direction (including lateral both
directions).
[0039] As shown in FIGS. 1 and 2, in the block body, there are
formed two through holes 21, 21 extending in parallel with a
predetermined distance from the upper and lower two rows of loaded
ball rolling grooves 19, 19, respectively, formed on both side
portions of the block body. Return passage constituting members 16,
- - - formed from a resin material and constituting ball return
passages are inserted into these through holes 21, - - - ,
respectively. On these return passage constituting members 16, - -
- , there are formed guide grooves 16a (guide portions) for guiding
a belt-like member of a retainer, mentioned hereinlater, so as to
extend in its axial direction (see FIG. 5).
[0040] The inner block 8 is formed with a U-shaped direction
changing passage for circulating the balls by connecting the loaded
ball rolling passage and the ball return passage. A circuit-shaped
ball circulation passage is composed by the loaded ball return
passage, the direction changing passage and the ball return
passage. Four, two in each lateral side, rows of such ball
circulation passages are formed. Each ball circulation passage is
formed in one plane so that the balls circulate in the ball
circulation passage two-dimensionally. To this ball circulation
passage, a guide portion for guiding the belt-shaped portion of the
retainer is arranged around the entire periphery.
[0041] The outer peripheral side of the direction changing passage
is formed on the end plate 18 as an outer peripheral side
constituting member of the direction changing passage, and the
inner peripheral side of the direction changing passage is formed
on the holding member as an inner peripheral side constituting
member of the direction changing passage. By combining these end
plate 18 and holding member 17, the guide groove (guide portion)
for guiding the belt-like member of the retainer in the direction
changing passage is formed.
[0042] FIGS. 6 to 8 represent the holding member. The holding
member 17 is provided with holding portions 24 extending along both
side edges of the loaded ball rolling groove 19 and preventing the
ball held by the retainer from coming off from the outer rail 7 at
the time of removal of the inner block 8 from the outer rail 7 and
provided with direction changing passage inner peripheral side
constituting portions 25, - - - , constituting the inner peripheral
side of the direction changing passage, disposed at longitudinal
both end portions of the holding portions 24. When such holding
member 24 is mounted to the block body 15, it cooperates with the
outer side surface of the block body 15 to thereby form the guide
portion 26 (guide groove) for guiding the belt-shaped member of the
retainer.
[0043] The holding portion 24 includes a first holding piece 24c
for holding the lower side of the retainer mounted to the lower
side ball circulation passage, a second holding piece 24b for
holding the upper side of the retainer mounted to the lower side
ball circulation passage and mounted to the upper side ball
circulation passage, and a third holding piece 24a for supporting
the upper side of the retainer mounted to the upper side ball
circulation passage. Each of the respective direction changing
passage inner periphery constituting members 25 has an
approximately semicircular-arc shape.
[0044] These holding members 17, 17, return passage constituting
members 16, - - - and end plates 18, 18 are independently formed
from resin material, which are then assembled with the block body
15.
[0045] As shown in FIG. 2, a number of balls 28, - - - supported by
the retainer 27 to be rotatable and slidable are accommodated in
each ball circulation passage. The retainer 27 is provided with a
plurality of spacers 30, - - - each disposed between the balls and
belt-shaped members 31, 31 connecting both side edge portions of
the respective spacers 30, 30 (see FIG. 10). The spacers 30, - - -
are formed so as to provide a cylindrical shape having an outer
diameter smaller than a diameter of the ball 28. Each of the
spacers 30 is formed, at its axial both ends, with spherical
recessed portions 30a, 30a as curved recesses each having a
curvature radius substantially equal to the radius of the ball 28
so as to correspond thereto. In an arrangement that the spacers 30,
- - - are disposed between the balls 28, - - - , the axes of the
spacers 30, - - - lie on the line connecting the centers of the
balls 28, - - - . The axial length of the spacer 30 is set to be
thin so that the interval of the adjacent balls 28, 28 has
necessarily minimum value.
[0046] The belt-shaped members 31, 31 have constant thickness and
are connected to both sides of the side surface of the spacer 30.
These belt-shaped members 31, 31 have flexibility so as to flexibly
cooperate with the direction changing passage. In an interfering
position of the belt-shaped members 31, 31 and the balls 28, - - -
, there is formed a cut-in portion having a curvature radius
substantially equal to the radius of the ball 28. The belt-shaped
members 31, 31 project over both the side edge portions of the
balls 28, and the projected portions are guided by the guide
portions formed in the ball circulation passages. Furthermore,
corner portions of the longitudinal both end portions of
belt-shaped members 31, 31 are formed so as to provide round
portions 31a, 31a. The spacers 30, - - - and the belt-shaped
members 31, 31 are integrally formed from synthetic resin material
through an injection molding process.
[0047] Hereunder, the screw portion of the linear actuator will be
explained. As shown in FIG. 1, the screw shaft 9 penetrates the
central portion of the inner block 8. On the outer peripheral
surface of the screw shaft 9, there is formed a ball rolling groove
9a for the screw shaft 9 as rolling member rolling groove for the
spiral screw shaft. This ball rolling groove 9a for the screw shaft
9 has a cross section formed into a gothic-arch including two
circular-arc portions having a curvature radius slightly larger
than the radius of a ball 33 for the screw shaft. On the other
hand, the through hole formed in the block body 15 is also formed
with a loaded ball rolling groove 15a for the screw shaft as loaded
ball rolling member for the screw shaft so as to correspond to the
ball rolling groove 9a for the screw shaft. This loaded ball
rolling groove 15a for the screw shaft 9 also has a cross section
formed into a gothic-arch including two circular-arc portions
having a curvature radius slightly larger than the radius of the
ball 33 for the screw shaft. A loaded rolling passage of the ball
circulation passage is composed of the ball rolling groove 9a for
the screw shaft 9 and the loaded ball rolling groove 15a of the
block body 15.
[0048] The ball 33 contacts the ball rolling groove 9a for the
screw shaft 9 at two points, and the ball 33 also contacts the
loaded ball rolling groove 15a for the screw shaft of the block
body 15 at two portions. That is, the ball 33 contacts the ball
rolling groove 9a and the loaded ball rolling groove 15a at four
points. Further, in order to apply a preload, there is adopted a
so-called over-size system in which a ball having an over-size
having a diameter slightly larger than the interval between the
screw shaft 9 and the block body 15.
[0049] A return pipe 34 for circulating the ball rolling between
the ball rolling groove 9a for the screw shaft 9 and the loaded
ball rolling groove 15a for the block body 15 is provided with the
inner block 8. This return pipe 34 constitutes a ball return
passage for the screw shaft (rolling member return passage for
screw shaft) communicating one and the other ends of the loaded
rolling passage.
[0050] The return pipe 34 has a circular cross section and is bent
by about 90 degrees at both end portions with respect to its body
portion so as to provide an approximately gate shape. The leg
portions thereof are not parallel to each other and their extending
directions are twisted respectively in accordance with lead angles.
Both the end portions of the return pipe 34 are formed with cutouts
for scooping up the balls rolling in the loaded rolling passage.
Both side portions of the return pipe 34 are fitted into the loaded
rolling passage with several pitches of interval. Furthermore, this
return pipe 34 is inserted from the lower surface side of the inner
block 8, i.e. on a side opposing to the upper surface of the outer
rail 7, and fixed to the inner block 8 by means of pipe holder. By
disposing the return pipe 34 to the lower surface side of the inner
block 8, a portion on the upper surface side of the inner block 8
can be freely utilized, thus making easy the assembling working of
a table or like.
[0051] A number of balls 33, - - - for screw shaft are arranged in
the loaded rolling passage. A number of spacers 35, - - - are also
arranged each between the balls 33. The spacers 35 are formed so as
to provide a cylindrical shape having an outer diameter smaller
than a diameter of the ball 33. Each of the spacers 30 is formed,
at its axial both ends, with spherical recessed portions as curved
recesses each having a curvature radius substantially equal to the
radius of the ball 33 so as to correspond thereto. In an
arrangement that the spacers 35, - - - are disposed between the
balls 33, - - - , the axes of the spacers 35 lie on the line
connecting the centers of the balls 23, - - - . The axial length of
the spacer 35 is set to be thin so that the interval of the
adjacent balls 33, 33 has necessarily minimum value.
[0052] When the screw shaft 9 is rotated, the balls 33, - - -
rolling in the circumferential direction in the loaded rolling
passage under the loaded state are scooped up by one front end of
both end portions of the return pipe 34. The scooped-up balls 33
pass through the inside of the return pipe 34 and return again to
the loaded rolling passage from the other one front end of both the
end portions of the return pipe part from the one end by several
pitches. The balls 33 circulate in a manner reverse to that
mentioned above by reversing the rotating direction of the screw
shaft 9.
[0053] FIG. 9 shows a perspective view of the balls 33, - - - and
spacers 35, - - - which are arranged in the ball circulation
passage of the screw portion and FIG. 10 shows the balls 28, - - -
and retainer 27 which are arranged in the ball circulation passage
of the guide portion. The arrangement of the spacers 35, - - - and
30, - - - having recessed portions corresponding to the curved
surfaces of the balls 33, - - - and 28, - - - between these balls
33, - - - and 28, - - - permits to prevent the metal balls from
being contacted to each other and realize a low dust and low noise
generation structure.
[0054] As shown in FIG. 10, the balls 28 move two-dimensionally on
a plane in the ball circulation passage of the guide portion. That
is, the balls 28 circulate in the order of the linear loaded
rolling passage A.fwdarw.the U-shaped direction changing passage
B.fwdarw.the linear return passage C.fwdarw.the U-shaped direction
changing passage B. In the direction changing passage B, the
belt-shaped member 31 of the retainer is freely bent. Since a
number of spacers 30 disposed in the guide portion are connected in
series to each other by the belt-shaped members, the balls 28 can
circulate in the predetermined track and, hence, unnecessary
contacting of the balls 28 to the surrounding circulation passage
can be prevented. Furthermore, since the belt-shaped members 31 are
guided by the guide portions formed to the ball circulation
passage, the belt-shaped members 31 can circulate in the more
constant track, and hence, the spacers 30, - - - connected in
series by the belt-shaped members 31 and the balls 28 disposed
between these spacers 30 can also circulate in the more constant
track.
[0055] Particularly, in the case where the return passage
constituting members 16, the holding members 17 and the end plates
18 are molded independently with resin material different from the
metal block body, only the loaded rolling passage and the balls are
metal-to-metal contacted. Thus, the generation of dust or like can
be preferably suppressed.
[0056] On the other hand, with reference to FIG. 9, the loaded
rolling passage D in the screw portion is formed into spiral shape
and the ball return passage E (return pipe) is circumferentially
twisted in the advancing direction of the balls 33 as mentioned
before. That is, in the screw portion, the rolling directions of
the balls 33 and spacers 35 are three-dimensionally changed and
moved in the complicated manner. The unnecessary contacting of the
balls 33 to the surrounding circulation passage can be prevented by
separating the spacers 35 without connecting them with the
belt-shaped member. In addition, the spacers 35, each having curved
recesses at its both end portions corresponding to the curved
surface of the ball 33, are arranged in the screw portion without
using conventional spacer balls, so that the distance between the
adjacent balls can be shortened in comparison with the case of
using the spacer balls. Accordingly, the number of balls 33 which
can receive the load is not reduced.
[0057] The linear actuator of the characters mentioned above will
be assembled in the following manner with reference to FIG. 2.
[0058] First, the screw shaft 9 is inserted into the block body 15
and balls 33, - - - and spacers 35 - - - are then alternatively
accommodated and arranged in the space between the screw shaft 9
and the block body 15. The balls 33 and spacers 35 are also
accommodated and arranged in the return pipe 34. The return pipe 34
is then mounted to the block body 15. In thus manner, the
assembling of the block body 15 and the screw shaft 9 is
completed.
[0059] Next, the return passage constituting members 16, - - - are
inserted into the through holes 21 of the block body 15, and the
holding members 17, 17 are assembled to both the side surfaces of
the block body 15. Then, the end plate 18 is mounted to one end
surface of the block body 15. In the next step, the balls 28, - - -
arranged and held by the retainer 27 is inserted in the ball
circulation passage of the guide portion from the side opposing to
the mounting side of the above-mentioned one end plate 18, and the
other end plate 18 is thereafter mounted to the other one end
surface of the block body 15. Finally, the inner block 8 is
forcibly fitted into the outer rail 7 and the housings 13 and 14
supporting both the ends of the screw shaft are fastened to both
ends of the outer rail 7.
[0060] Further, it is to be noted that tubular rollers may be used
as rolling members in substitution for the balls.
[0061] As mentioned hereinbefore, according to the present
invention, a plurality of spacers, each formed at its both ends,
with curved recessed portions corresponding to the curved surface
of the rolling member, are disposed between the rolling members of
the guide portion, and these plural spacers are connected in series
by the belt-shaped members having flexibility. On the other hand, a
plurality of spacers, each formed at its both ends, with curved
recessed portions corresponding to the curved surface of the
rolling member, are disposed between the rolling members for the
screw shaft of the screw portion in a manner separated from each
other. The mutual contact between the respective metal rolling
members can be prevented by disposing the spacers, having recessed
portions corresponding to the curved surfaces corresponding to the
rolling members, arranged in the guide portion and the screw
portion. Furthermore, since the plural spacers arranged in the
guide portion, in which two-dimensional motion is carried out, are
connected to each other in series by the belt-shaped members, the
rolling members circulate in the constant track, and unnecessary
contacting of the rolling members and their surrounding circulation
passage can be prevented. In the screw portion, the twisting motion
around the advancing direction is required as well as the
two-dimensional and three-dimensional direction changing motions,
so that unnecessary contacting of the rolling members and their
surrounding circulation passage can be prevented by separating the
spacers without connecting the spacers by the belt-shaped members.
Thus, since the mutual contact of the rolling members and the
unnecessary contacting of the rolling members and their surrounding
circulation passage can be prevented, low generation of dust or
like and low generation of noise can be realized.
* * * * *